Cold tube bending and sizing



Feb. 14, 1961 D. E. ARMSTRONG EFAL 2,971,556

- cow TUBE BENDING AND SIZING Filed Nov. 12, 1959 2 Sheets-Sheet 1 IN VEN TOES David E Bmflrorg ORNE Y Feb. 14, 1961 D. E. ARMSTRONG EIAL2,971,556

cow TUBE BENDING AND SIZING Filed Nov. 12, 1959 2 Shets-Sheet 2CflMPRESS/ON 121/?50 T/ON 1 l8 TENS/0N H3724.

D/AE C Tl ON 4 7' GAP 0,? l/NSUPPORTED AREA INVENTORS 56 David E.Elmira/2g 2 Tlwmas JJ Damn -59 WaZZer 1i: ZZ4Z'6H/ I go 1. BUGS e1ATTORNEY United States PatefitO COLD TUBE BENDING AND SIZING David 'E.Armstrong, Cherry Lane, Doylestown, Pm; Thomas J. J. Dunn, 9809 BurwoodSt., Philadelphia County, Pa.; Walter H. Stulen, 17 Hamilton Drive E.,North Caldwell, NJ.; and Gerald 'P. Bucks County, Pa.

Filed Nov. 12, 1959, Ser. No. 852,462

20 Claims. (Cl. 153-32) The present invention relates generally to amethod and apparatus for simultaneously cold-forming and cold sizing ofopenended metal tubular material to its final shape in a shaping dieunder opposing forces within the leading edge and against the trailingedge of the tubular workpiece and is specifically adapted for themanufacture of open-ended tubular fittings of metals from open-endedmetal blanks which are diflicult to cold-form and coldsize in theshaping die by reason of the hardness of the metal or by reason of theseizing and galling characteristics of the metal against the die undercold-forming conditions.

Roeser, Lahaska,

ing'causes upsetting of the hard metal.

Patented Feb. 14, 1961 2 by the flow of metal in the tube blank duringcold-form- By use of a. freely floating lead guiding member within theworkpiece the fiow of metal is such that upon completion of the formed90 L the opposite side of the blank has been flowed forwardly to besquare with the leading bevel of the tubular blank. If the metal flow isrestricted by shouldering at the leading edge, then the upsetting of thehard metal which occurs results in the production of wrinkles, thickenedareas and unduly thinned areas in the-finished fitting which cannot beremoved while maintaining the desired dimensional tolerances of theformed product. 1

The prior art recognizes that wrinkling readily occurs duringcold-forming of hard metals having relatively high tensile strength inthe order of about 70,000 p.s.i. 'It is not practical to try to iron outin hard metals, such as stainless steel, wrinkles which are caused byupsetting of the metal. Once the hard metal has been upset and wrinkled,the metal cannot readily be thereafter mechanically smoothed to size inthe cold and cannot be smoothed in heated condition without completelyaltering the structure of the metal. It is the microstructure of themetal which alfects the metallurgical characteristics and the physicalproperties of the metal and heating alters this structure.

The present invention is an improvement over the method disclosed inPatent No. 2,907,102 to two of the inventors herein.

The apparatus of the present invention differs mainly from that inPatent No. 2,907,102 in respect to the utilization of'a multiple partmandrel formed of elastomeric material, said multiple part mandrelhaving end-retaining sections formed of homogeneous hard elastomer and amiddle section of soft homogeneous elastomer. The hard elastomer endsections of the multiple part mandrel have a critical modulus ofelasticity within a relatively narrow range, and further have a limitedrange of hardness to provide a brake-shoe type of frictional engage-jment of the retaining end sections in direct contact with the innerwalls of the open-ended tubular stock whereby extrusion of the softmiddle section is prevented under the extremely high pressures which aredeveloped within the tube during forming and sizing. These end sectionsare further characterized by a good elastic memory to permit thesefrictional engaging end sections to quickly recover and return to theiroriginal shape for easy removal from the finished tubular product and bereused in the multiple mandrel assembly for mass production.

' The method and apparatus of the present invention enable the rapidproduction of uniformly formed and sized product from tubular stock ofhard metals and metals which are subjected to seizing and galling asillustratively shown in Tables A nad B below, with practically no wasteof the metal.

The art has long recognized the distinction between the cold-forming ofhard metals of the type as shown in Tables A and B below and therelative ease of coldforming of metals which are soft and have goodlubricity, such as, for example, copper, copper base alloys, zinc andzinc base alloys. In the case of the soft metals or metals of goodlubricity, cold-forming operations are carried out prior to a separatesizing.

Wrinkling and buckling occur with the hard-or seizing metals in theregion of the smallest radius during forming to a 45, 90 orl80 L which.is readily ironed out steps to make the metal malleable andductile.

Thus, a cold-forming operation carried out for hard metals readilywrinkles the hard metal and it is necessary thereafter to iron outthewrinkles by processes involving heating. The ironing process suggestedin the prior art requires a series of heating and mechanical workingIroning which must therefore-be carried out'at high tempera? turesdefeatsthe entire purpose of the present invention which is expresslydesigned to carry out a forming and sizing operation in the cold.

The present invention provides a freely floating leading element whichacts entirely within the tubular blank and which first transmitscounter-thrust locking pressure to the multiple part mandrel to causethe self-locking multiple part mandrel to come into brake-shoe lockingengagement under the counter thrust, pressurizing during the sizingoperation for soft metals but which cannot be carried out for hardmetals.

- It isa-necessary requirement of the present invention that the leadingedge of the hard tubular blank metalwhich is beveled at the start ofcold-forming dare not be restrained by shouldering or spherical cappingwhere- TABLE A Metals exhibiting high seizing and .galling'characteristics against hardened steel die surfaces Zirconium andzirconium alloys Titanium and titanium alloys Stainless steel Carbonsteel Cobalt and cobalt alloys Aluminum and aluminum base alloys TABLE BMetals, alloys and related metallic mixtures of high hardness hithertonot capable of being cold-formed into standard fixtures withoutwrinkling, upselting and fracturing Tantalum and tantalum alloysTitanium and titanium alloys Tungsten and hard tungsten alloysMolybdenum and hard molybdenum alloys Cobalt and cobaltalloys-Hz'astelloy B, Hastelloy C Cobalt-alumina Cermets containing upto 40% of cobalt;

or cobalt alloy and.6 A1 0 Cermets Harder metals listed under Table Aabove, when cold-. formed in accordance with the invention require theapplication of a pushing force for cold forming, this pushing forcebearing against the trailing edge of the workpiece and the trailing hardend of the multiple part mandrel of about 1000-1500 pounds.

Softer metals such aslisted under Table B above require lower pushingforces for cold-forming. For exam ple with an aluminum workpiece, thepush force may be as low as about 500-600 pounds for /24" diametertubular stock.

The manufacturing methods of the invention accomplishes simultaneouscold-forming and sizing of fittings. which meets standard specificationsof the type used .for stainless steel fittings. These standardspecifications widely used at the present time for hard metals include:

(0) M88. Standard Practice SP-43-1956 for Stainless Steel Butt-WeldingFittings, developed and approved by the Manufacturers StandardizationSociety of the. Valve: and Fittings Association, New York 17, NY.(originallyapproved Oct. 1950).

(b) ASA No. B3619 Specification'for Austenitic Stainless Steel Pipe,American Society of Mechanical Engineers, 29 West 39th Street, New Yorkcity.

Rapid. forming operations can be carried out by copper tube. bendingapparatus as taught inv United States patent to Arbogast; No; 2,701,002granted February 1,

1 955; Arbogastspush ram element for forcing the tu-' buiar blankthrough the die, supports the trailing edge of theblank while thesupporting headpiece engaging the die, thisArbogast apparatus is unableto cold-form seizing metals of the type'which are listed in Table Aabove or to cold-form hard metals of the type which are listed in TableB without wrinkles.

Cold-forming andsizing of the hard metals and seizing metals are carriedout in accordance with-the invention by employing a multiple partmandrel of elastomeric material which is constructed as a self-containedunit to come into frictional-engagement at its ends, wholly within theinterior of the tube blank, tomaintainthe mandrel in fixed frictional orbrake-shoe type of engagement wholly within the tubular blank throughoutthe entire coldforming and cold-sizing operation. 3

Thus it is a feature of the invention to eliminate entirely thesupporting engagement. of the metal lead piece of Arbogast with theleading. edge of the tubular workpiece, and to rely upon the multiplepart elastomer mandrel under pressure from thejfiexible forcetransmitting linkage delivering hydraulic counter thrust for sealingthe: mandrel during the coldsforming and cold-sizing operation.

The invention includes an improved flexible forcetransmitting linkagefor transmitting the opposing hydraulic force to the multiple. part:elastomer mandrel while the tubular workpiece: with themandrel insertedtherein is being formed in the.die. by theforWard thrust of thehydraulic ram.

nected interfitting ball and socket hat-shaped members which are drivenby the counter thrust hydraulic ram. At the head of the new linkage is aguiding lead member which is placed entirely within the workpiece forengaging the front face of the multiple part elastomer mandrel.

- The novel, lead guiding member of the invention is a free-floatingmetal part in counter thrust engagement for actuating the self-lockingmultiple part mandrel. guiding member is constructed to be freelymovable within the tubular blank before bending and yet can be fulcrumedduring cold-forming to direct the metal flow. The lead member freelyenters into the tubular blank under action of the opposing counterthrust force during the preliminary pressurizing operation and induceslocking of the leading edge of the multiple part mandrel by its pressureaction. The lead member is constructed with a spherical face at itsouter edge which subsequently contacts the bent portion of larger radiusof the cold-formed tube. The spherical face acts as a fulcrum during thecold-forming operation directing the flow of metal at the inner tubewall of the maximum radius and helps to tilt the lead member around thecurved portion of the die cavity. This spherical face permits a slidingaction and obviates metal thinning in the tubular region of largerradius which ordinarily occurs under tensile forces during forming. Thefreely floating lead member is also constructed with a flat or planarface at its inner edge with relation to the bent portion of smallertubular radius to direct metal flow within thisportion of the tube wallas it thickens during the cold-forming operation.

During the initital pressurizing operation, the selfsealing multiplepart mandrel within the blank is anchored. at the forward end of thetubular blank by the pressurizing force transmitted exclusively by theinternally located free-floating lead member. As a result;

of, the forward movement of the workpiece, which is urged intocold-formed condition by the forward push ram, the flow of metal in thethickened inner radius is directed around the curve of the die by thetilting of the lead guiding member during forming. This action is carried out as a result of the flat contact of the planar surfaceto theinner radius of the tubular work while the spherical sliding surface atthe outer radius of the bent tube fulcrums the metal flowing action bylever movement about the center pivot of the lead member which moves,valong the axis of the tubular blank.

The invention also provides a new flexible force transmitting linkagecomprising an assembly of unconnected,

interfitting ball and hat shapedmembers for transmitting counter thrusthydraulic forces to the lead member within the workpiece and thus, tothe front face of the multiple part mandrel. during simultaneouscold-forming and cold-sizing of the tubular workpiece in the die.

An object of the invention is to provide a new free floating lead memberfunctioning entirely within the work, and mechanically engaging thefront face of the multiple part mandrel to maintain itself and themandrel within the workpiece throughout the cold-forming andcold-sizing. operation under opposing forces within the die- A furtherobject of the invention is to provide an improved linkage for the freefloating lead member uniquely adapted tonegotiatc the sharp angle ofbending.

A further object of the invention is to provide a linkage for the freefloating lead member which is constructed to provide longer service lifeof this member.

A further object of the invention is to provide a new multiple partelastomer mandrel for insertion into-the tubular work' whichisself-locking under pressure action by internally directed counterforces.

' The multiple part mandrel, uniquely constructed for cold-forming ofhard metal tubular stock, is characterized by self-sealing endsoperative under pressure to pre- This. new linkage comprises an assemblyofunconvent extrusion. of the soft middle part. The mandrel,

This

while exerting uniform internal pressure on the inner walls of thetubular stocks, controls the flow of the metal, preventing upsetting ofthe metal and prevents wrinkling during the bending and sizingoperation.

A further object of the invention is to provide a new multiple partelastomer mandrel formed of materials hav-' ing superior physicalproperties of resistance to abrasion, elastic memory, toughness,compressibility, and frictional engagement for the interior wall of thetubular workpiece to thereby provide a long lasting mandrel capable oflong repeated use in production.

A further object of the invention is to provide a new coaction of themultiple part mandrel of the invention in' combination with the newflexible force transmitting slidably movable within the die. Thiscombination is adapted to pressurize and lock the multiple partelastomer mandrel solely by counter thrust pressure.

It is a characteristic of the multiple part elastomer mandrel of theinvention that the form of the mandrel need not be tapered at itsleading edge. It is preferred that the ends of the mandrel be squaredoff for alignrnent with, the force transmitting members at the forwardand rearward positions of the oppositely directed bydraulic thrustmembers. It is surprising that the hard end sections containing the softmiddle unit are able to completely withstand the tearing and abrasiveforces due to the interior irregularities of the workpiece which causedestruction of the unitary rubber mandrel of the type as used in theArbogast Patent No. 2,701,002 during very rapid forming operations underhigh pressure.

The non-tapered multiple part mandrel is assembled in accordance withthe invention from separate mating sections of hard elastomeric endpressure sealing members and a soft elastomeric middle section. Thesesections are merely dropped into the workpiece. The forming operationcan be carried out in an ordinary hardened steel die. The thinning whichordinarily occurs at the larger radius of the bend is substantiallyobviated with the mandrel of the invention and the thickening whichordinarily occurs in the region of smaller radius is confined to a verysmall segment of the are.

For example, using the multiple part self-contained pressure sealingmandrel in the apparatus of the invention for the shaping of 2" tubeblanks of stainless steel into full 90 Us, and with a wall thickness forthe tube blank of 0.109 inch, it has been found that an increase in wallthickness of 37 /z% based on the initial thickness occurs in the regionof smallest radius. At the same time the thinning in the correspondingregion of greatest radius which is due to tensile forces is at mostabout 5-10% of the original thickness of the tubular blank. Thus, theflow of metal is adequate to prevent thinning of the metal at theoutside portion of the bend by maintaining the permissible wall gaugerequirement of the accepted industry standard referred to above.

It is an important characteristic .of the multiple part mandrel of thepresent'invention in. comparison with the mandrel of the patent to twoof the present inventors, Patent No. 2,907,102, that the multiple partmandrel may be used again and again without being mangled, cut, and'eroded by surface irregularities and without cracking due to repeatedcompression and elastic recovery in continuous production. H

ofthemandrel ofthe invention which are preferably formed-of a vinylchloride resin plastisol baked at elevated The softer, readilycompressible middle section of the multiple part mandrel is formedpreferably of soft natural rubber, synthetic compounded rubber, orpolysulfide rubber which is adjusted in known manner by'formulation to ahardness value varying from about a Shore Hardness Rating to about 5 to60 on the Shore A scale and which has a modulus of elasticity which isless that 54 the value of the hard end sections.

The service life of the softmiddle section when made of natural rubberin terms of number of stainless steel fittings made is from about2000-4000 pieces depend ing upon the skill of the operator. The servicelife of polysulfide rubber is about 1000 to 2000 pieces.

In contrast, the use of a single or unitary mandrel, whether made ofnatural rubber, synthetic rubber such as neoprene, 'butadiene-styrenepolymer, etc., or vinyl e. V ,For, example, the service. life of thehardzendsections resin plastisol, etc., as disclosed by the prior PatentNo. 2,907,102 there is achieved a service life of only about 3 fittingsin the hands of an unskilled operator. This can be improved to 10fittings in the hands of a skilled operator atfer which the mandrel hascompletely deteriorated.

It has been found that the modulus of elasticity of the hard mandrel endmembers of elastomer material must decrease in proportion to the ratioof cross sectional area taken at the external diameter of the tube tothe wall thickness.

ticity of elastomer end pieces is required. For example,

with /2" to 4" pipe a suitable range of E will lie between 10,000 toabout 20,000 p.s.i.

Limits for the modulus of elasticity of the mandrel end pieces inrelation to tube cross-sectional area (O.D.) are listed in Table Cbelow, the data given for stainless steel pipe.

TABLE C Pipe size: E (p.s.i.) /2" to 1" inclusive 15,000-25,000 Above 1"to 2" inclusive 10,000-20,000 Above 2" to 3" inclusive 5,000-10,000Above 3" 300-5,000

In smaller sizes of standard tubing, wall thickness in proportion tocross-sectional area increases and the tendency for the soft middlesection to extrude also increases. For this reason the preferred Evalues for thicker tubes of smaller diameter is close to 20,000 p.s.i.

Corresponding Shore Durometer D values for these pipe sizes are shown inTable D.

At Durometer D hardness above the end piece tends to fracture.

'Preferred materials for vinyl resin plastisol which is best due to itsexcellent elastic memory, urethane rubber, cast epoxy resin, and otherelastometer materials such as hard rubber either natural or synthetic.These other elastomer rubbers may be formulated to provide the necessarypropertieswithin the specified limits for hardness and modulus-ofelasticity. Other and further objects of the present-invention willappear from the more detailed description set forth below, it beingunderstood that such more detailed description is given by way ofillustration and explanation;

Thus, with a small ratio of cross sectional area to wall thickness ahigher modulus of elas-' the mandrel end pieces include.

7. only and not by way of limitation, sinceva-rious changes. therein maybe made by those skilled in the ,art without. departing from the scope.and spirit of the present invention.

In connection with the more detailed description, there is shown in thedrawings,jin

Fig. 1 is a fragmentary elevationalview of an appara tus embodying ourinvention:andadaptedfor useiimprac ticing our method with partsbeing-broken awayandu-im section to illustrate structural details.

Fig. 2 is a fragmentary view-ofgone of the diernem= bers with a workblankand the'forming mechanism in an initial positionwith partssectioned and .brokenaway. for convenience; in illustration.

Fig. 3 is a fragmentaryview: with one-of'the diemembers removed,illustrating the apparatus in. fully actuated position in whichposition-the tubular blank has. been formed to angled shape;

Fig. 4 is a fragmentary viewpartly in section along line 44v of Fig.2showing-rone'type'of link whichmay be used for connecting the innermetalt guiding member to. the hat-shaped leading elementengageablewiththe flex ible hat-shaped elements in theforce transmitting assembly.1

Fig. 5 is a side elevational 'view partly in section illustrating amodified form' of ball'and'socket joint- Fig. 6 is a vertical sectionalview on line 6-6 of Fig. 5.. v Fig. 7 is a diagram for purposes ofmathematical analysis, illustrating the physical forces and factorsafiecting the forming of hardmetals. I

Fig. 8 is a diagram showing, for purposes of mathematical-analysis, theelastic and plastic propertiesof the. tube material;

Fig. 9 is a diagrammatic showing for purposes of mathematical analysis.

Figs. 10:: andlOb are diagrammatic showings of shear deformationaifectingbuckling and wrinkling.

Figs. 11a and 11b are diagrammatic showingsof factors affecting bucklingand wrinkling.

Fig. 12 is a diagrammatic view illustrating the-forces exerted at theleading edge 'ofthe work for the purpose of demonstrating internalbrake-shoe frictional forcesagainst the inner surface of the workpieceand counter thrust pressurizing forces parallel to'the longitudinalsurface of the workpiece.

Figs. 13 and 14 illustrate in diagrammatic fashion by side viewandbottomview, respectively, a special form of beveled and tapered tubularworkpiece which allows a distribution of, forces within the. die with nowaste of workpiece material.

Fig. 15 is a side elevational view partly in section illustrating amodified form of ball and socket joint.

Fig. 16 is a vertical sectional view on line 16-46 of Fig. 15.

Referring now to Figs. 1-3, inclusive, a tubular Workpiece 18 is showninserted within the entrance portion of a die cavity 15 formed by a pairof hinged dies, lower die member 13 and upper die member 14, these diemembersbeing connected by pins 17 and. supported by lower support 11 andupper support 12, which with the hydraulic mechanism are hired to themain frame of the press (not shown).

Within the-tubular workpiece 18 thereis inserted the multiple partelastomer mandrel of the invention. The mandrel as shown in Figs. 2 and3 comprises hard elastomer end sections 22a and 22b, one of which is inforce bearing relation to the forward push ram 19 and the other 225 inforce bearing-relation to-counter-thrust ram 23. The other hard mandrelend section 22b is brought into frictional locking engagement againsttheinterior wall of the tubular workpiece at the forward or leading endof-the workpiece as a result of the application of a pressurizing forceby the counter-thrust ram 23 acting through the flexible forcetransmitting meansand the internal prcssurizing, and aligning leadpiece.

The middle sections 22' and 22" of the multiplepart elastomer mandrelare each soft in comparison with the hard end sections-22a and 22b and.are distinguished from these hard end sections'by performingthefunction-of a fluid under pressure whentheentire mandrel is confinedwithin the workpiece and the workpiece and mandrel are subjected to'highpressures.

Each tubular workpiece 18 cold-formed and cold-sized, in accordancewith-the invention is forced through: die cavity 15-and curved diecavity 16under the simultaneous application of pressure. by forward pushram 19 and counter-thrustram 23 actuated by a hydraulic force fromcylinder 25.

The forward and rearward movement of push ram 19 is controlled by thehydraulic mechanism shownin Fig. 1' of applicants Patent No. 2,907,102and this mechanism forms no part of the present invention.

With the ram'19'fully retracted and the four-wayxvalve. in port closingposition rotated about 45 from the position shown in' Fig. 1 in" Patent.No. 2,907,102, the pump unit is energizedfor'flow of hydraulic fluidthrough a relief valve, a check valve and by. the line into therighthand and of the cylinder 36 associated with ram 19. Fluid pressureis developed aginst the piston which moves to the left in cylinder tobuild up pressure on the multiple part mandrel- The: pressure build-upon the multiple mandrel occurs by. reasonv of the movement of aligningmember 27' against the multiple part mandrel 18, and

particularly against the leading'hardened end section: 22b

of the mandrel.

Thus, with shoulder20 of the push ram 19 coming into force bearingrelationship at bearing surface 21 against the trailing end faceofthe'hard end-section 22a of the mandrel (see Fig:- 2), the multiplepart mandrel is brought to an initial-pressurized condition. Toinitially pressurize the multiple mandrel the required movement issmall, of the order of Arof an inch (see Fig. 2 for initialpressurizing). When this pressure attains a predetermined value, of theorder of SOO-GOO pOunds-per" square inch, the four-way'valve of Fig. 1,Patent No. 2,907,102, is moved to a position to admit fluid pressurefrom pump by way of associated'lines to'the upper end of the cylinderassociated with ram'19 to applyagainst the piston a forming pressure ofthe order of about 550-l,500 pounds'per square inch. Since the formingpressure of push ramI19 exceeds that of' the mandrel pressure ofcounter=thrust ram 23, there willbe movement of the tube workpiece :8auto the forming position of the die cavity 16 at the The pressureapplied by the pistons to the push ram 19 and counter-thrust ram 23 maynow be simultaneously increased and equalized in order to raise thepressure on the multiple part mandrel and upon the formed tubularworkpiece 1-8. The pressure applied to the piston for the push ram 19 isincreased'by raising the setting on the relief valve from 500-600 poundsper square inch to about 1,500 pounds per square inch. By suitablyadjusting the settings of these relief valves any desired differentialof pressure may be applied to the tube workpiece dependinguponthe'materials of the workpiece and anydesired final finishing orsizing pressure may likewise be established (see Fig. 3 forcold-forming). It will be understood that particular pressures will beselected. on the basis of the hardness and seizing properties of themetal material and the wall thickness of the tube work; piece.

Each of the elastomer'mandrel sections,- the soft cen-. tral-section22", the adjaceutmiddle sections 22'and the hardened sections have aform approximating the in ternal form. of the-tubular blank to beslidably movable within the workpiece for -easy= removal after forming:About inch clearance is convenient. Each of thes'e sections ischaracterized by good-elasticrecovery'to'peF mit repeated' reuse; Eaclr'of the sections is" tough to" 9 withstand repeated abrasion incold-forming andcoldsizing. Each of the sections is homogeneous andreinforcing agents may be used to impart toughness. Sponge rubber cannotbe used because of its tendency to tear after one cold-formingoperation, particularly due to abrasive forces caused by surfaceirregularities of the interior of the tubular workpiece; hence it ispreferred that the mandrel sections be non-porous.

Radial expansion of hardened end sections 22a and 22b locks the entiremandrel within the tubular workpiece by brake-shoe engagement againstthe internal surface of the workpiece under the opposing pressurizingforces. This radial expansion prevents extrusion of the soft elastomersections 22' and 22" shown for the five- 22b against the internalsurface of the tubular workpiece during pressurizing and cold-formingoperations is based solely upon the frictional forces between theradially expanded end sections and the material of the tubularworkpiece. The middle sections move relative to the 10 engagement withthe guiding element" 50 and the hat shaped member 60. The ball andsocket connections 54, 59 and 61, Figs. 5, 6,: l5 and 16, are preferred{to-the cross-link. connection 24 of Fig. 4 since these. are longerlasting and providemore uniform action in their directing action formetal flow under cold-forming by the free floating leading member 27.The guiding member 56 in the embodiments shown in each of these Figs. 5,6, and 16 is fitted with spherical end 54 to ball socket 59 in theleading element. A similar hall and socket close fit is provided by theother end of the rod terminating in spherical ball portion 54 which'fits in the spherical counterbore 61 of the hat-shaped member 60. Thespherical dome of the hat extends'from the annular edge of bat member 60to engage the annular socket or counterbore of an adjacent hat-shapedmember31 in the assembly as shown in Figs. 2 and 3. In Figs. 5 and 6snap rings 62 and split washers 63 lock the ball ends 54 of theconnecting rod in place in the socket 59-of the lead internal surface ofthe workpiece during pressurizing and forming operations but the endsections are substantially fixed.

The counter-thrust pressure applied against the leading hard end section22b of the multiple part mandrel is transmitted through the flexibleassembly of unconnected hat-shaped members 31 which are located in thebend channel portion 16 of the shaping die as shown in Figs. 1-3.

A novel lead element is interposed between the flexible assembly ofhat-shaped members 31 and the mandrel hard end section 22b, this elementcomprising a metal flow guiding element 27 which is located whollywithin the tubular workpiece 18 as shown in Fig. 2 and adjacent theleading tapered edge thereof, this guiding element 27 being linked to ahat-shaped member 31 by a connecting rod 28. One surface of the guidingelement 27 is planar or flat for directing metal flow along the minimumradius of bend in the die. The opposite surface of the guiding element27 is spherical to contact the area of maximum radius of bend in thedie. The spherical face acts as a fulcrum during the cold-formingoperation directing the flow of metal at the inner tube wall of themaximum radius and helps to tilt the lead member around the curvedportion of the die cavity.

The connecting rod 28 shown in Fig. 4 is one species 1 guiding element27 lies wholly within the workpiece 18.

The length of the connecting rod 28 is equal to the radius of the diecavity 16 at the bend. If this length is substantially less than theradius, the pin would jam and the workpiece .would jam at the bend-16inthe die.

cavity. If the rod lengths were substantially larger than v this radius,the rodwouldsnapwhen the work and mandrel move under cold-workingpressure around the bend.

Two types of leading element which 'are' preferred are shown in Figs. 5and '6 and Figs. 15 and 16. In each of these types the connecting rod 52is in ball and socket guiding element 50 and hat member 60,respectively. In Figs. 15 and 16 set screws 71, 72, 73 and 74 in bores75, 76, 77 and 78 perform the function of the snap rings and washers.The embodiment of Figs. 15 and 16 is preferred to that of Figs. 5; and6, the set screws providing longer service life than the-rings.

By lubricating the forming surfaces and using a metal dissimilar fromthat of the tube workpiece, the friction developed during-the formingisdecreased. diiferen; tial of pressure of the order of 0 1,500 p.s.i. isadeg quate for the bending of tube workpiece formed-9fv the hardest ofmetals to the desired dimensions of curvature.

The usual lubricating compounds utilizedfor dieswill be found suitablefor cold-forming the harder and seizing metals. Preferred lubricantsinclude 'Houghton Draw Oil No. 3105, chlorinated rubber solid filmlubricant (up to 40-50% chlorine) and carnauba wax emulsion lubricant.Such lubricants as molybdenum ,disulfide; linseed oil, white lead,linseed oil oil-white lead graphite, and lard oil are not satisfactorysince they give rise to seizing and galling in the die. V

Each tubular workpiece is open-ended and of a beveled length to keep toa minimum the loss of material in the final finishing operation. The endof the tube workpiece 18 engaged by the pressure member 19 does notrequire any finishing operation-since the end surface thereof ismaintained essentially flat and square by the engagement thereof withthe shoulder 17a. At the leading end of the tube workpiece 18 only asmall amount of metal need generally be removed to bring it to its finaldimension of a flat and square surface.

Generally, the tubular workpiece is beveled at one end and square at theother end in order to permit cold: forming and cold-sizing without lossof material. The

- bevel is such that the flow of the material of the workpiece along theshorter dimension brings the metal to a substantially square edge afterforming.

In Figs. 13 and 14 there is shown a preferred beveled tubular workpiecein which the shorter length moves forward during the cold-formingoperation.

In order to distribute the pressure on the front end of the tubularblank as it passes the die split, a fiat spot is ground on the tube asshown in these figures. This flat spot 2 prevents excessive pressure onthe front end 4 of the tubular blank of Figs. is an -14;

The following example illustrates the bending of stain less steel tubing304 in accordance with the invention and brings out' thejphysi cal-relationship of'IiiiSlYfdfej restraining force,'"reaction"force andfriction force for bending ,of' hard, metals. i Eff-$113;

Reference is made to Figs 7-14 for the diagrammatic representation ofthe mathematical factors. I

Mathematical. analysis (a) PROBLEM 'The problem illustrated inthis-examle is 'tdlfomr a straight'tube into a 90 L. The equations developedherein are applicableitoany' size and the example given below appliesto-a stainless tube of the following dimensions:

'd =2.'37'5'ii1..

NOMENCLATURE P=push force in pounds P =restraining force in pounds Pgreacti-on force at outside'turn-in pounds F5=friction force caused byreaction force P in pounds F friction force causedby tube expansion(this is in addition to F p=coefiicient of friction t=initialwallthickness'of tube r': outside radius of tube in inches R;=-in sideradius of bend in-inches- R =mean radius of bendin inches R=outsideradius of bend in inchesp=mandrel pressure in p.s.i. rg=insideradius of tube v =angle between P3 and P E=rnodulus of elasticity of'tube material in p.s.i. M=moment required to bend tube in inch-pounds A=inside area of tube in square inches Si=ultiinate tensile strength ofmaterial in p.s.i. S=ultimate compressive strength of material inp.s.-i. S =tensile yield strength of material in p.s.i. fi -compressiveyield strength of material in p.s.i. E;=fricti0n caused by burstpressure on push side-pounds ii -friction caused by burst pressure onrestraint side S=in'side surface area oftube in square inches 7=Poissonsratio v (0) EFFECT OF INTERNAL AND EXTERNAL PRESSURE Withthe tubefree inthe die, the burst stress and radial expansion may'be readily computedby standard formulae from the internal pressure.

In this example:

. et'cris' larger than the die cavity. The flow pressure of stainless"steel 304 is about equal to the ultimate tensile strength or may beabout 20% higher; Thus, the greatest pressure will occur when the flowpressure causes a circumferential compressive yield and flow which u henl..134.='0.0034 (or about0007" interferenceonthe diameter) Accordingly apreferred fit in the-"die is a-clearanceof Arr-about .001. V i

1.2 The corresponding pressure is:

,OO0 .l'09 p 1.134 =8 640 p.s.i.

To this pressure is added the internal mandrel pressure at aninterference of 0.007 on diameter or greater then The external frictionis then equal to:-

F'= SX/1-(8640+P)=Su(8640+%) (4) In this example:

S =6 6-sq. in. A =3.65sq. in. .=.20 (bad lubrication) =.05 (goodlubrication) A solid film lubricant, chlorinated paraflin (50% chlorine)was used with u=0.05.

(d) VALUES OF F ARE NOW SHOWN ASA FUNCTION OF LUBRICATION Pressure,p.s.i.

Qr=.20)Bad-lubricati0n 121,200 147,000 166,800 (p=.05) Good lubrication31,800 36,800 41,700

A value of p=2500 p.s.i. may be taken to be typical and the forceF=735200 ,u.

(e) MOMENT TOBEND'TUBE Reference is made to Fig. 8. For a firstapproximation it maybe assumed that the tube material is an idealelastic-plastic material with no work hardening property. Also, it maybe'assumed that the yield point in tension is the same as that incompression and that all strains are sufiiciently large to be in theplastic range. On this basis the moment resisting the bending may bereadily computed as follows. for a thin-wall tube:

P =P ,(sin (H- cos 6.) P ==P (cos 0-;rsin 0) 2M R. 0 I E'TiI SKSquaring'the first two equations and adding Since is not likely to begreaterthanOJS then P3EVPO2+P12 1 W e can get an approximate solution bynoting-that .the resulting moment is 'Since P ranges from 8,000 to20,000 pounds the Wrinkling and buckling Reference is made to Figs. aand 10b.

' Wrinkles are caused by buckling of the tubes where the compressivestresses exceed the local column strength. Along the side AA thecompressive stresses are the highest. Buckling will occur if thesestresses are too high and the internal pressure of the rubber is notsufficient. From this source, the wrinkles are to be expected to be atright angles to the axis of the tube. This is shown in Fig. 10b.However, due to the lesser compression (or even tension) along BBcompared to the'high compression along AA, there is a shear type ofdeformation as shown by the exaggerated sketch in Figs. 11a and llb.This shear deformation causes compressive stresses that are at 45 to theaxis of the tube and cause a buckling'that is in the direction as shownin Fig. 11b.

' From the foregoing it is seen that there are two sources of thebuckling forces. tial compressive stresses that are introduced frompinching the tube in the die from an oversize tube. Furthermore, themain axial compressive stresses are in creased from the frictionalforces from an oversize tubel .There is one method of preventing localbucklingand this is by employing suflicient internal pressure. Ofcourse, the condition leading to buckling may be-greatIy alleviatedbymaintaining very low frictional forces: (by proper lubricant and havingsmooth surfaces ondie and tube). 1

An estimate of the required internal pressure is made by taking a oneinch square surface of the tube and. assuming the axial forcecorresponding to the compressive yield of the material. The compressiveforce is equal to:

. cx Y If there isa local eccentricity or bow of 0.005 inch,

For y =100,000 and t=0.109, this moment is 54 .5 in. lbs.

' :In upsetting practice, the free length of a bar should not exceedabout 3 /2 diameters to prevent buckling. This length is'about 0.4 inchof plate. The laterally in duced moment is I x pa 4000 p.s.i,

A third cause is the circumferen- 5 '14 The force F; to give this is P=1r/4 2.08?=13,800 lbs.

Equation 12 gives the friction developed when the inter- 5 ference isgreater than about 0.007 inch. Very high push forces are needed toovercome this friction which developed when the leading edge of thetubular workpiece made of hard metal negotiates the curve in the diecavity, Although the push force may be loweredsomewhat by suitablelubricants, high values of push force are still needed due to friction,particularly when the lubrication is inadequate. If P is the force onthe end of the tube (excluding the rubber pressure) thecompressivestress in the metal is of the push stress 8 Since r isroughly equal to r,-,, then stress s=l/t,u(8640+'p)' (15) Typical valuesare t 1.=. =0.05 to'0.20 I p=l500 mm Y 7 stress s=1,000,000 L Then ifthe coeflicient of friction exceeds about 0.09, compressive yield orupset occurs! when the force is first applied.

From the present example it is seen'that an initial interference fitwill cause a large increase in the push load. This increase under badlubrication can easily be as high as 60 tons. However, even when thelubrication is fairly good, a heavy interference will cause buckling ofthe tube because of upsetting. No frictional forces (other than that atthe reaction P will exist'if the tube is about 0.002 inch to 0.003 inchloose in the die.

M andrel pressure The-corresponding end force is 1 P= A,=ss00 3. s.-2-1,20010s. 3

It can therefore be seen that the pushforce s'hould not bear too heavilyon the mandrel or excessive burst will occur on the tube, to cause metalupset.

v Loss of rubber pressure p V There is a loss of rubber pressure duetofi'iction peg tween the unlubricated rubber and the tube. See-Fig. 12,

This is calculated as follows; e A dp=21rnpndx The limiting Example:

r =l.08 x= V V 3.56 p =4000 p.S.i. p=4000 1470 540 '='0.3

P 400 X e-- x This shows that the rubber pressure drops rapidly withdistance. .If there is a poor fit between shoulder 20 and the hardtrailing end 22a, soft rubber from 22' may eXtrude rearwardly' into thegap or unsupported area shown in Fig". 12'. p

The 2 inch tube of this example is pressurized under 7 a force of 500pounds and cold worked into a 90 L by The steps of Example I werecarried out with Hastelloy B tubing, 2 inch pipe size, under formingpressure of 1,600 pounds and mandrel locking pressure of 500' pounds.

A perfect 90 L was made.

EXAMPLE III The steps of Example I were carried out with aluminumtubing, 2 inch pipe size, under forming pressure of 600 pounds andmandrel locking pressureof 500 pounds.

A perfect 90 L was made.

EXAMPLE IV The steps of Example I- were carried out with titaniumtubing,f2 inch pipe size, under forming pressure of 1600 pounds andmandrel locking pressure of 500 pounds.

A perfect 90 L was made.

EXAMPLE V The steps of Example I were carried outwith zirconium tubing,2 inch pipe size, under forming pressure of 1600 pounds and mandrellocking pressure of 500 pounds.

A perfect 90 L was made.

Modifications of this invention not described herein will-becomeapparent to those skilled in the art; Therefore,= it is intended thatthe matter contained in the foregoingdescription and the accompanyingdrawings be interpretedas illustrative and not limitative, the scope ofthe invention being defined in the appended claims.

In each of the foregoing examples a'five part mandrel was used as shownin Figs. 2 and 3, the center part 22" of the multiple part mandrel.being Thiokolrubber filled with zinc sulfide and being softest, theintermediate adjacent section's-22"being natural rubber which is harderthan the Thiokol rubber and the hard end sections being vinyl chlorideplastisolin a ratio of 68/32 vinyl chloride resin totricresyl phosphateplasticizer, baked at 400 F.

to shore hardnes's'o'f" 65 D. Other plasticizers, for'example dibutylphthalate and dibutylfsebacate may be used to attain preferred shortDhardness values of 55-75 and the modulus of elasticity values indicated'lfer'e'inbeforeand the formulation proportions maybe adjusted for lowerhardness values, e.g; 12-55 with elasticity'values from about 300 to25,000 p.s.i.

We claim:

l. A method of simultaneously cold-forming and coldsizing open-endedtubular workpiece to its final shape without upsetting the 'material andwo'rkpiece in a shaping die comprising inserting a removably expansiblemultiple part elastomer! mandrel having the same cross-sectionalexternal shape as the intemal cross-sectional shape of said workpieceand being easily slidable into and through said workpiece, said multiplepart mandrel comprising end sections having a modulus of elasticitylying between about 300 to 25,000 pounds per square inch, a hardnessvalue on the Shore Durometer" D scale of between about 12 and 75 andgood elastic recovery and a middle section of soft elastomer having goodelastic recovery, applying a pressurizing force within said workpieceagainst the front face of said mandrel while pushing against the otherend of the workpiece to thereby expand the end sections at the frontface, and locking the mandrel in position for cold-forming, applying acold-forming force against the trailing edge of said workpiecewhilemaintaininng; the

pressurizing force against the front face of said mandrel to force saidworkpiece through said die thereby coldforming and cold-sizing saidworkpiece.

2. A method as claimed in claim 1 wherein said workpiece is formed of ahard material which is flowed by a guiding member forwardly of theleading edge of said mandrel to thicken said material uniformly at theinner internalv radius of bend of the formed final shape.

3. A method as claimed in claim 2 wherein said uniform flow of thethickened material is carried out, by application of a flat guidingsurface to the inner thickened portion of the formed tube and whereinsaid flat guiding surface is fulcrumed at the bend from a fulcrum whichis opposite to the thickened section, said uniform thickening takingplace under the action'of the pushing force and the pressurizing forceagainst said mandrel. o

4. A method as claimed in claim 2- wherein said tubular workpiece isbeveled to provide a shorter workpiece length at the inner radius offorming-and a longer workpiece edge atthe outer radius of forming, saidlonger edge becoming shorter under the application of pushing andtensile forces during cold-forming to be square at the leading edge ofthe workpiece with the shorter edge in the cold-formed workpiece.

5. A method as claimed in'claim 4 wherein-said mandrel is pressurized bycounter-thrust forces within said workpiece acting on the front face ofsaid mandrel by force transmitting and aligning means, the center ofsaid force transmitting and aligning means being on the axis of saidworkpiece.

6. A method as claimed incl'aim 5 wherein-the'center of said forcetransmitting and aligning means for said counter-thrust pressurizing.force for said mandrel is in alignment with both the'forward edge ofsaid shorter beveled length and the forward edge-of said longer beveledlength of the workpiece before cold-forming.

7. A methodas' claimed in claim 6.wherein'said-tubular workpiece is flatat its longestedge'to provide a hat tapered spade section at theouter'portion'of the longest cdgeato provide more uniform distributionof forces on the workpiece. within the die;

8. A method as claimed in claim 6 wherein said counter-thrustpressurizingiforce is about 500-600 p0u'nds andsaid pushing: force isabout 600 :to about 1500 pounds;

9.: A method-as claimed in claim 8 whereinsaidworkpiece is lubricatedwith a chlorinated hydrocarbon solid film lubricant, said counter-thrustpressurizing force being about 500 pounds. and said pushing-fo'rceiwhich is larger than said counter-thrust force being; about 600pounds to cold-form a workpiecemade of aluminum.

10. A method as claimed in claim 8 wherein said workpiece is lubricatedwith a chlorinated hydrocarbon solid film lubricant, said counter-thrustpressurizing force beingabout" 500 pounds a and said pushing force whichis larger than said counter-thrust force being 'at' least about 1500pounds to'cold-form a workpiecemade of stainless steel.

11. Apparatus for simultaneously cold-forming and cold-sizing an openended tubular workpiece to its final shape without upsetting thematerial of the workpiece in a shaping die comprising a removablyexpansible mul- 17 tiple part elastomer mandrel having the samecross-sectional external shape as the internal cross-sectional shape ofsaid workpiece and being easily slidable into and through saidworkpiece, said multiple part mandrel comprising end sections having amodulus of elasticity lying between about 300 to 25,000 pounds persquare inch, a hardness value on the Shore Durometer D scale of betweenabout 12 and 75 and good elastic recovery and a middle section of softelastomer having good elastic recovery, said mandrel being locked infrictionally fixed position within the workpiece under the pressurizingaction of a force applied within the workpiece against the front face ofthe mandrel and a greater cold-working force applied against thetrailing edge of the workpiece and mandrel.

12. Apparatus as claimed in claim 11 wherein said multiple part mandrelcomprises end sections of hard polyvinyl chloride plastisol and a middlesection of soft elastic rubber.

13. Apparatus as claimed in claim 11 wherein said multiple part mandrelcomprises end sections of hard polyvinyl chloride plastisol and a middlesection of soft elastic polysulfide rubber.

14. Apparatus as claimed in claim 11 wherein said multiple part mandrelcomprises five parts, there being two end sections of hard polyvinylchloride plastisol, in termediate sections of soft elastic rubber and acenter section of soft elastic polysuliide rubber, said centrallylocated polysulfide rubber being softer than said intermediate sectionsof rubber.

15. Apparatus for simultaneously cold-forming and cold-sizing an openended tubular workpiece to its final shape in a shaping die underopposing forces acting within the leading edge and against the trailingedge of said workpiece comprising a removably expansible multiple partelastomer mandrel having the same cross-sectional external shape as theinternal cross-sectional shape of said workpiece and being easilyslidable into and through said workpiece said multiple part mandrelcomprising end sections having a modulus of elasticity lying betweenabout 300 to 25,000 pounds per square inch, a hardness value on theShore Durometer D scale of between about 12 and 75 and good elasticrecovery and a middle section of soft elastomer having good elasticrecovery, in combination with pressurizing and aligning means deliveringa counter-thrust force to the front face of said mandrel within saidworkpiece while pushing said workpiece and mandrel at the trailing edgesof both, said mandrel being locked in frictionally fixed position withinthe workpiece by the brake shoe action of the end sections under thepressurizing section of the force applied through said pressurizing andaligning means within said workpiece against the forward end section ofsaid mandrel.

16. An apparatus for cold-forming and cold-sizing as claimed in claim 15wherein said pressurizing and aligning means contain flexible forcetransmitting means adapted to deliver a pressurizing counter-thrust to aflexible mandrel within the tubular workpiece, said force transmittingmeans comprising an assembly of a plurality of unconnected identicalhat-shaped members, each of said hat-shaped members being constructed ofan annular base defining a socket in said base, said annular baseslidably fitting within the die cavity, and a socket engaging sphericaldome portion opposite said base adapted to fit into and bearingly engagethe socket of the adjacent member during forced passage of saidunconnected assembly through the bend of the die while cold-forming andcold-sizing.

17. Apparatus as claimed in claim 15 wherein a guiding member for metalflow is provided in advance of said mandrel, said member having a fiatmetal flow guiding surface adapted to direct the metal flow duringcoldforming against the inner thickened portion of the formed workpiecein advance of said mandrel and wherein said directing surface isfulcrumed at the bend of the die from a fulcrum opposite the thickenedportion, said guiding for said thickened portion taking place under theac tion of the pushing force and the pressurizing force against saidmandrel.

18. Apparatus as claimed in claim 17 wherein said fulcrumed oppositeportion of said guiding member is spherically shaped and said guidingmember is linked to said pressurizing and aligning means by a ball andsocket.

19. Apparatus as claimed in claim 18 wherein said ball and socketincludes a connecting rod whose length is shorter than the shortestradius of bend of the work piece.

20. Apparatus as claimed in claim 11 wherein said tubular workpiece isformed of a metal which exhibits seizing and galling characteristicsagainst steel and wherein the internal forming surfaces of said die aremade of hardened steel.

References Cited in the file of this patent UNITED STATES PATENTS1,978,452 Fladin Oct. 30, 1934 1,993,361 Cornell Mar. 5, 1935 2,701,002Arbogast Feb. 1, 1955

